The general aim of this project is to identify and study the function of factors that regulate vertebrate embryonic development. This is being approached in three ways. One approach is to analyze the regulation and function of one of the vertebrate homologs of the Drosophila gene Distal- less. In flies this gene regulates limb and sensory appendage formation. The frog and mouse homologs are both expressed in epidermis, branchial arches, and in gradients in the limbs. The mouse gene is also active in hair follicles, tooth primordia and other locations. DNA elements and protein-DNA interactions responsible for this expression pattern are being mapped. In addition, targeted inactivation and mis-expression studies are being used to test for the function of Distal-less gene expression in the epidermis of transgenic mouse embryos. A second approach employed has been to clone mRNAs encoding receptor-type protein kinases that are expressed in specific tissues of early frog embryos. One such kinase, called Pagliaccio, has been shown to affect cell-cell adhesion when constitutively activated in Xenopus embryonic ectoderm. A related gene, TCK, is also being studied. The third approach focuses on the developmental function of calcium- dependent cell adhesion molecules in the zebrafish neural tube. A partial cDNA encoding a novel cadherin, VN-cad, has been cloned, sequenced, and characterized by in situ hybridization. When the complete protein coding region has been obtained for this gene, functional studies will be carried out in zebrafish embryos.